Purpose of side vents on aftermarket front bumpers?
12-30-07 | 01:47 PM
#26
2/4 wheel cornering fiend
Joined: Nov 2002
Posts: 3,090
Likes: 3
From: Pasadena, CA
Re: the negative pressure, assuming the oil ducts are vented openly to the wheel well, and you have a normally shaped fender (not concave); would there be sufficient enough negative pressure generated to vent the air in the wheel well out of the fender vent (that's normally used for the oil cooler vent)? Assuming you enlarged the vent too... Or would that be not such a good idea, and going w/ the concave fenders is the way to go? Not sure if the former would involve too much turbulence/inadequate vent size, etc.
12-30-07 | 02:07 PM
#27
Thread Starter
Joined: Jul 2003
Posts: 13,216
Likes: 4
From: Tampa, FL
I hope it isn't coming across that way...
Note that I stated I never was saying outright that the RE Amemiya vent was effective. BUT:
The underhood area is in itself a higher pressure area than most of the area above the hood, because pressure is being built up from the front intake. Thus, if it was an area of equal pressure or below, you'd still get benefits from the vent.
The underhood area is in itself a higher pressure area than most of the area above the hood, because pressure is being built up from the front intake. Thus, if it was an area of equal pressure or below, you'd still get benefits from the vent.
I know you're just making numbers up for the sake of discussion, but I don't think many people appreciate the magnitude of the pressures we're discussing here.
The static pressures measured across the top of the hood would be in the order of a few hundred pascal's, compared to atmospheric pressure of 101,325Pa at sea level. So a measured static pressure of 250Pa (which is realistic) is only ~0.25% of atmospheric pressure. Dynamic pressure at 100mph is ~1200Pa, which is a lot higher than the static pressure but still only a small fraction of atmospheric pressure (~1.2%).
The static pressures measured across the top of the hood would be in the order of a few hundred pascal's, compared to atmospheric pressure of 101,325Pa at sea level. So a measured static pressure of 250Pa (which is realistic) is only ~0.25% of atmospheric pressure. Dynamic pressure at 100mph is ~1200Pa, which is a lot higher than the static pressure but still only a small fraction of atmospheric pressure (~1.2%).
A wheel well by itself doesn't generate that much negative pressure, so any vent that can help evacuate air from the wheel well can't hurt in that case.
The concaved fender generates a lot of turbulence as well as neg pressure, so it can go either way depending on other factors.
12-30-07 | 02:26 PM
#28
2/4 wheel cornering fiend
Joined: Nov 2002
Posts: 3,090
Likes: 3
From: Pasadena, CA
I wondered about that as well...the tradeoff between negative pressure & turbulence, as I've seen how many of the land speed cars (including the RacingBeat FD) cover the wheel wells due to the tremendous turbulence they noted from that area (and if I'm not mistaken, many of the smaller hybrid vehicles also partially cover the rear wheel wells for the same reason, because less turbulence results in better gas efficiency, yes?)
12-30-07 | 02:40 PM
#29
Thread Starter
Joined: Jul 2003
Posts: 13,216
Likes: 4
From: Tampa, FL
You're talking about the difference between direct airflow from the oil coolers versus a slight negative pressure area in the wheel wells.
Less turbulence means less aerodynamic drag, the main goal of land speed vehicles.
Thanks again
~Ramy
